Although the incidence of gastric cancer has declined in the U.S., it is still the second leading cause of cancer deaths in the world. Little is known about its causative factors, partly due to the fact that most studies have usually focused on just one or two potential risk factors. The primary objective of this 5-year population-based, case-control study is to test the hypothesis that Helicobacter pylori infection, a low serum pepsinogen I/II ratio, a high salt or nitrite intake, a low intake of specific fruits and vegetables and a family history of gastric cancer, separately or in combination, identifies a subject at high risk for this disease. A total of 436 cases and 436 controls are expected to be interviewed with collection of a blood sample during the study period. Eligible cases will be diagnosed at the 9 largest hospitals with histological confirmation of their diagnosis. One population-based control will be frequency-matched to each case by sex, age (within 5 years) and ethnicity (Caucasian, Chinese, Filipino, Hawaiian/part-Hawaiian or Japanese. A comprehensive dietary questionnaire with about 250 food items will be administered to each study participant. It will estimate the usual dietary intake of specific food items as well as the intake of nitrate, nitrite, nitrosamines, sodium, vitamin C, alpha-tocopherol, and beta- carotene. In addition to the dietary data, the questionnaire will include the following: family history of cancer, including gastric cancer; past medical history of gastric or duodenal ulcer, gastric polyps and gastric surgery; cigarette smoking history; use of vitamin supplements. The slides of each case will be reviewed by a pathologist for histological typing (intestinal or diffuse type). The following tests will be done with the blood sample: Helicobacter pylori IgG antibody assay, H. pylori cytotoxin antibody assay, pepsinogen I and II levels, and ABO blood typing. Analysis of data will consist of an assessment of the dose-response relationships, either separately or in combination, of nitrite intake, salt intake, vitamin C intake, specific fruit and vegetable intake, H. pylori antibody levels to gastric cancer. Unconditional logistic regression analyses will be done to estimate the odds ratios. This investigation will contribute to our understanding of the role of dietary factors, H. pylori infection and family history in the etiology of gastric cancer. The findings should provide useful information towards the primary prevention of this disease.